He is best known for his 1984 book on persuasion and marketing, Influence: The Psychology of Persuasion. It was based on three "undercover" years applying for and training at used car dealerships, fund-raising organizations, and telemarketing firms to observe real-life situations of persuasion. He found that influence is based on six key principles: reciprocity, commitment and consistency, social proof, authority, liking, scarcity.[4] In 2016 he proposed a seventh principle. He called it the unity principle. The more we identify ourselves with others, the more we are influenced by these others.[5]

The book has sold over three million copies and has been translated into thirty languages.[6] It has been listed on the New York Times Best Seller list and Fortune lists it in their "75 Smartest Business Books".[7] It is mentioned in 50 Psychology Classics.[8][9]

One of Cialdini's other books, Yes! 50 Scientifically Proven Ways to Be Persuasive, was a New York Times Bestseller; and another of his books, The Small BIG: Small changes that spark a big influence, was a Times Book of the year.[10] Cialdini's most-recent book is Pre-suasion, which was published in 2016.